Question: If $2a + 7b + 5c = 4$ and $x + 9y = -5$, what is $-40c + 8x + 72y - 16a - 56b$ ?
Explanation: $= -16a - 56b - 40c + 8x + 72y$ $= (-8) \cdot (2a + 7b + 5c) + (8) \cdot (x + 9y)$ $= (-8) \cdot (4) + (8) \cdot (-5)$ $= -32 - 40$ $= -72$